1. Field of the Invention
The present invention relates to a font managing apparatus for a character generator in which plural font pattern data are stored.
2. Description of Prior Art
Conventionally, the character generator of bit map type has been well known. In the character generator of bit map type, each character is formed as a bit image on a bit map memory according to font pattern data stored in a font memory. In a character generator of bit map type, fonts of several kinds are selectably stored in the font memory. In order to increase the number of selectable fonts, interchangeable font cartridges each of which has a ROM or character generator together with a command for designating a font. The character generator transforms each of transmitted code data into a bit image consulting with pattern data of the designated font. Bit images thus formed are sent to a printer and, thereby, the document is printed out in accordance with the designated font.
In a character generator which provides a variety of interchangeable font cartridges, an area for registering management information of individual fonts is provided for managing available fonts in a system RAM. Upon starting the character generator or when one or more font cartridges are interchanged, respective management information of available fonts is registered or renewed into the font managing area of the system RAM.
As a memory for memorizing font data which is provided in a font cartridge, a rewritable RAM is used other than a ROM. As a rewritable RAM, a RAM backed up with a back up power source is desirably used to hold font data even when the character generator is turned off. The RAM of this type has an external by operable input switch and font data is considered to be loaded down thereinto from the host computer as far as the external input switch is switched on.
If the switch is switched off or in the case of a font RAM which does not provide a back up power source, font data can be loaded down thereinto from the host computer.
In a character generator wherein plural font cartridges are settable and interchangeable, there is a possibility such that the font cartridge presently selected is drawn out or moved to another slot even when editing operation of character images is executed.
In such a case, it becomes necessary to reselect a font to be used.
Conventionally, when the font cartridge in use is drawn out, a font cartridge set in the slot adjacent to that of the drawn out font cartridge is selected automatically. However, if the font is reselected in this way, the font is changed one to another on the way of printing and this worsens quality of print.
In another conventional character generator, the operation thereof is automatically stopped as an error when the font cartridge in use is drawn out. In this case, it becomes necessary to load down font data again in order to start the suspended printing operation. Upon loading down font data, if a command for selecting a font contained in neither of font cartridges having been set is entered, it is processed as an error which urges to cancel it.
In the character generator of this type, a font is designated by appointing a slot number or a font name. Accordingly, it becomes necessary for an operator to have a preliminary knowledge of the slot number or font name regarding the desired font. However, it is difficult to designate the desired font exactly since each font is defined by attributes of font such as font name, pitch (print width), point (height of character), weight (print thickness) and the like which are unfamiliar to an ordinary user. This invites miss operation often.
In a font memory contained in a font cartridge, directory of font data which includes address information with respect to font patterns corresponding to character codes is also stored. Upon accessing the font memory, address information of a font pattern corresponding to a character code sent from the host computer is read out from the directory at first and, thereafter, the font pattern designated by the address information is read out. Accordingly, it is always needed to access the directory of the font memory every character. This access operation is done parallel to imaging operation of characters and, therefore, access time becomes long. This fairly limits the processing time.
In JP-A 116551/1986, there is disclosed a font managing system wherein address information of directories of individual font memories is stored as a directory address table in a system RAM in order to manage directories. Upon accessing a font pattern, the directory address table is accessed at first and, then, the corresponding font pattern stored in the font memory is read out.
If the memory area to be assigned to the directory address table is reasonably narrow so as to shorten the addressing time, character imaging operation can be executed at a high speed.
However, in JP-A 116551/1986, directories of all available fonts are registered in the directory address table of the system RAM. Due to this, the system RAM must have a large volume.